1. Field of the Invention
The present invention relates generally to airfoils in a gas turbine engine, and more specifically to an insert located within a cooling air passage of a vane.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a turbine section in which a hot gas flow from the combustor passes into and reacts with multiple stages of rotor blades and stationary vanes or nozzles to extract mechanical energy from the engine. The efficiency of the gas turbine engine can be increased by providing a higher gas flow temperature. However, the temperature is limited to the materials used and the effective amount of cooling provided in the first stage of the turbine. Thus, to improve the efficiency of the engine, more effective cooling of the first stage of the turbine would be necessary if the materials used do not change. More effective use of the cooling air requires less cooling air bled off from the compressor, resulting in a more efficient compressor and therefore more efficient engine.
Since the stationary vanes are not rotating like the rotor blades, the vanes make use of inserts supported within the hollow space formed by the vane wall. Inserts provide for a cooling supply channel and, through a plurality of strategically placed cooling holes, provide impingement cooling on the inner wall of the vane. Impingement cooling of the inner wall of the vane is an effective method of transferring heat from the vane to the cooling air, since the cooling air is basically shot directly against the wall surface, resulting in a high turbulent flow.
U.S. Pat. No. 4,697,985 issued to Suzuki on Oct. 6, 1987 and entitled GAS TURBINE VANE discloses a turbine vane with a wall forming a hollow inside, and an insert supported within the hollow wall by ribs and spaced therefrom to form a cooling passage for cooling air. The insert includes a plurality of orifices that provide impingement cooling against the inner vane wall surface. The insert forms a single cooling supply passage within the vane and as a result requires a large amount of cooling air in order to eject air through all of the impingement holes. Another problem with this type of insert that is that, as the air is injected through the holes and into the flow channel (between the vane wall and the insert), the air must flow toward the trailing edge to escape. Allot of air builds up in the downstream direction and acts to prevent air passing out through the holes to impinge against the wall. Thus, the impingement effect is reduced and therefore the cooling effect is lower.
Some airfoils use multiple inserts in multiple cavities, such as U.S. Pat. No. 5,511,937 issued to Papageorgiou on Apr. 30, 1996 entitled GAS TURBINE AIRFOIL WITH A COOLING AIR REGULATING SEAL which discloses a turbine vane with a fore and an aft cavity each having an insert therein with impingement holes, the two cavities being separated by a rib. This multiple cavity design will reduce the above described cross flow problem, but still requires the large amount of cooling flow to eject air from all of the impingement holes.
U.S. Pat. No. 4,252,501 issued to Peill on Feb. 24, 1981 entitled HOLLOW COOLED VANE FOR A GAS TURBINE ENGINE discloses a vane with a vane having a forward section and a rearward section separated by an apertured web (23 in this patent), the forward section having a first tube (insert) and the rearward section having a second tube (insert). The second tube is divided into two cavities by a partition (31), with one of the cavities facing the suction side and the other cavity facing the pressure side. Cooling air supplied to the first tube provides impingement cooling to the forward section, then passes through the apertured web and into the suction side tube, and then through the impingement holes to provide impingement cooling to the suction side wall of the rearward section. A separate supply of cooling air is delivered through the pressure side cavity in the second tube and through holes to provide impingement cooling for the pressure side wall in the rearward section. The Peill patent shows the basic concept of multiple insert cooling of the present invention, but still requires a large amount of cooling air, and also is not as efficient as the present invention design.